Stereoselective P(III)-Glycosylation for the Preparation of Phosphinated Sugars.

Most of the reported work focus on the development of O-, N-, C- and S-glycosylation methods. However, no study explores P(III)-glycosylation reaction. Herein we describe a convenient protocol to realize P(III)-glycosylation process.

Asymmetric Amination of Unstrained C(sp)-C(sp) Bonds.

The asymmetric functionalization of unstrained C(sp)-C(sp) bonds could be a powerful strategy to stereoselectively reconstruct the backbone of an organic compound, but such reactions are rare. Although allylic substitutions have been used frequently to construct C-C bonds by the cleavage of more reactive C-X bonds (X is usually an O atom of an ester) by transition metals, the reverse process that involves the replacement of a C-C bond with a C-heteroatom bond is rare and generally considered thermodynamically unfavorable. We show that an unstrained, inert allylic C-C σ bond can be converted to a C-N bond stereoselectively via a designed solubility-control strategy, which makes the thermodynamically unfavorable process possible.

Stereoselective Synthesis of Polysubstituted Dihydropyrroles via 1,5-Addition and N-1,4-Addition Cascade.

An unprecedented 1,5-addition/N-1,4-addition cascade reaction is established via palladium hydride catalysis. A variety of polysubstituted dihydropyrrole skeletons are constructed in high yield and with exclusively >20 : 1 diastereoselectivity. An enantioselective protocol of this design is also developed to provide a novel access to enantioenriched dihydropyrroles.

Asymmetric copper-catalyzed alkynylallylic monofluoroalkylations with fluorinated malonates.

The unprecedented copper-catalyzed asymmetric alkynylallylic monofluoroalkylation reaction is described the use of 1,3-enynes and fluorinated malonates. A series of 1,4-enynes bearing a monofluoroalkyl unit are achieved in high yields, excellent regio- and enantioselectivity and high selectivity. The asymmetric propargylic monofluoroalkylation is also developed.

Palladium-Catalyzed Asymmetric -1,5-Addition with Oximes via Hydroximation of Unsaturated Esters.

Different from electronically matched 1,4- and 1,6-additions, herein, we disclose an electronically mismatched 1,5-conjugate addition process with oximes as the nucleophiles. By this design, the oxime moieties are readily introduced to the γ-position of the electron-deficient substrates in good yields, excellent regioselectivities, and high enantioselectivities. The corresponding allyl oximes are also conveniently transformed into a series of valuable enantioenriched skeletons.

Asymmetric Substitution by Alkynyl Copper Driven Dearomatization and Rearomatization.

Catalytic asymmetric transformations by dearomatization have developed into a widely applicable synthetic strategy, but heavily relied on the use of arenes bearing a heteroatom. In this case, the dearomatization is facilitated by the involvement of a p-orbital electron of the heteroatom. Different from the conventional substrate-dependent model, here we demonstrate that the activation by a d-orbital electron of the transition-metal center can serve as a driving force for dearomatization, and is applied to the development of a novel asymmetric alkynyl copper facilitated remote substitution reaction.

Asymmetric formal sp-hydrocarbonations of dienes and alkynes via palladium hydride catalysis.

Transition metal-catalyzed asymmetric hydrofunctionalizations of unsaturated bonds via π-ƞ substitution have emerged as a reliable method to construct stereogenic centers, and mainly rely on the use of heteroatom-based or carbon nucleophiles bearing acidic C-H bonds. In comparison, sp carbon nucleophiles are generally not under consideration because of enormous challenges in cleaving corresponding inert sp C-H bonds. Here, we report a protocol to achieve asymmetric formal sp hydrocarbonations, including hydroalkenylation, hydroallenylation and hydroketenimination of both 1,3-dienes and alkynes via hydroalkylation and Wittig reaction cascade.

Enantioselective Palladium-Catalyzed Directed Migratory Allylation of Remote Dienes.

Chain walking has been an efficient route to realize the functionalization of inert C(sp )-H bonds, but this strategy is limited to mono-olefin migration and functionalization. Herein, we demonstrate the feasibility of tandem directed simultaneous migrations of remote olefins and stereoselective allylation for the first time. The adoption of palladium hydride catalysis and secondary amine morpholine as solvent is critical for achieving high substrate compatibility and stereochemical control with this method.

Ligand-Dictated Regiodivergent Allylic Functionalizations via Palladium-Catalyzed Remote Substitution.

Different from classical allylic substitutions that require a vicinal leaving group, an olefin bearing a remote leaving group is scarcely viewed as a potential allylation substrate. Herein, we describe feasible protocols to achieve regiodivergent allylic C-H functionalizations via palladium-catalyzed remote substitution, which provides a novel strategy for the seldomly studied migratory Tsuji-Trost reaction. Dictated by a suitable ligand, a process that involved 4,3-hydrofunctionalization of the generated conjugated diene intermediate via metal walking is observed in generally >20 : 1 regioselectivity.

Catalytic Asymmetric Hydroalkoxylation and Formal Hydration and Hydroaminoxylation of Conjugated Dienes.

The straightforward construction of stereogenic centers bearing unprotected functional groups, as in nature, has been a persistent pursuit in synthetic chemistry. Abundant applications of free enantioenriched allyl alcohol and allyl hydroxylamine motifs have made the asymmetric hydration and hydroaminoxylation of conjugated dienes from water and hydroxylamine, respectively, intriguing and efficient routes that have, however, been unachievable thus far. A fundamental challenge is the failure to realize transition-metal-catalyzed enantioselective C-O bond constructions via hydrofunctionalization of conjugated dienes.

Umpolung Asymmetric 1,5-Conjugate Addition via Palladium Hydride Catalysis.

Electronically matched nucleophilic 1,6-conjugate addition has been well studied and widely applied in synthetic areas. In contrast, nucleophilic 1,5-conjugate addition represents an electronically forbidden process and is considered unfeasible. Here, we describe modular protocols for 1,5-conjugate addition reactions via palladium hydride catalysis.

Stereoselective -C,B-Glycosylation via 1,2-Boronate Migration.

A novel protocol is established for the long-standing challenge of stereoselective geminal bisglycosylations of saccharides. The merger of PPh as a traceless glycosidic leaving group and 1,2-boronate migration enables the simultaneous introduction of C-C and C-B bonds at the anomeric stereogenic center of furanoses and pyranoses. The power of this method is showcased by a set of site-selective modifications of glycosylation products for the construction of bioactive conjugates and skeletons.

Palladium-catalyzed regio- and enantioselective migratory allylic C(sp)-H functionalization.

Transition metal-catalyzed asymmetric allylic substitution with a suitably pre-stored leaving group in the substrate is widely used in organic synthesis. In contrast, the enantioselective allylic C(sp)-H functionalization is more straightforward but far less explored. Here we report a catalytic protocol for the long-standing challenging enantioselective allylic C(sp)-H functionalization.

Designing an intelligent monitoring system for corn seeding by machine vision and Genetic Algorithm-optimized Back Propagation algorithm under precision positioning.

Objective: To realize the regulation of the position of corn seed planting in precision farming, an intelligent monitoring system is designed for corn seeding based on machine vision and the Genetic Algorithm-optimized Back Propagation (GABP) algorithm.

Methods: Based on the research on precision positioning seeding technology, comprehensive application of sensors, Proportional Integral Derivative (PID) controllers, and other technologies, combined with modern optimization algorithms, the online dynamic calibration controls of line spacing and plant spacing are implemented. Based on the machine vision and GABP algorithm, a test platform for the seeding effect detection system is designed to provide a reference for further precision seeding operations.

Stereodivergent Synthesis of Tertiary Fluoride-Tethered Allenes via Copper and Palladium Dual Catalysis.

Herein we describe a protocol for the unprecedented stereodivergent synthesis of tertiary fluoride-tethered allenes bearing a stereogenic center and stereogenic axis via Cu/Pd synergistic catalysis. A broad scope of conjugated enynes are coupled with various α-fluoroesters in high yields with high diastereoselectivities and generally >99% ee. In addition, the four stereoisomers of the allene products ensure precise access to the corresponding four stereoisomers of the fluorinated hydrofurans via a novel stereodivergent axial-to-central chirality transfer process.

Borylation of Unactivated C(sp)-H Bonds with Bromide as a Traceless Directing Group.

A palladium-catalyzed alkyl C-H borylation with bromide as a traceless directing group is described, providing a convenient approach to access alkyl boronates bearing a β-all-carbon quaternary stereocenter. The protocol features a broad substrate scope, excellent site selectivity, and good functional group tolerance.

One-Pot Preparation of Tricyclo[5.2.2.0]undecanes via Cu-Catalyzed Asymmetric Carboboration of Cyclohexadienone-Tethered Allenes.

The Cu-catalyzed asymmetric carboboration of cyclohexadienone-tethered allenes has been achieved through regioselective β-borylation of the allenes and subsequent conjugate addition to cyclohexadienones, affording -bicyclic frameworks with acceptable yields and high to excellent enantioselectivities. Further conjugate borylation of the carboboration products proved to be a favorable kinetic resolution process, which improved the overall enantioselectivity. Finally, one-pot preparation of highly enantioenriched tricyclo[5.

Stereoselective synthesis of conjugated trienes 1,4-palladium migration/Heck sequence.

Conjugated trienes are ubiquitous structures in natural products and organic functional molecules. An efficient 1,4-palladium migration/Heck sequence was developed for the highly stereoselective synthesis of trisubstituent 1,3,5-trienes, which were found to undergo easy E/Z isomerization in the presence of light.

Palladium-catalyzed α-arylation for the addition of small rings to aromatic compounds.

Small, strained rings have rigid, defined conformations and unique electronic properties. For these reasons, many groups seek to use these subunits to form biologically active molecules. We report a generally applicable approach to attach small rings to a wide range of aromatic compounds by palladium-catalyzed α-arylation of cyclopropyl, cyclobutyl and azetidinyl esters.

Stereodivergent Construction of Tertiary Fluorides in Vicinal Stereogenic Pairs by Allylic Substitution with Iridium and Copper Catalysts.

Although much effort has been spent on the enantioselective synthesis of tertiary alkyl fluorides, the synthesis of compounds containing such a stereogenic center within an array of stereocenters, particularly two vicinal ones, remains a synthetic challenge, and no method to control the configuration of each stereogenic center independently has been reported. We describe a strategy to achieve such a stereodivergent synthesis of vicinal stereogenic centers, one containing a fluorine atom, by forming the connecting carbon-carbon bond with a catalyst system comprising an iridium complex that controls the configuration at the electrophilic carbon and a copper catalyst that controls the configuration at the nucleophilic fluorine-containing carbon. These reactions occur with alkyl- and aryl-substituted allylic esters and the unstabilized enolates of azaaryl ketones, esters, and amides in high yield, diastereoselectivity, and enantioselectivity (generally >90% yield, >20:1 dr, 97-99% ee).

Palladium-Catalyzed α-Arylation of Carboxylic Acids and Secondary Amides via a Traceless Protecting Strategy.

A novel traceless protecting strategy is presented for the long-standing challenge of conducting the palladium-catalyzed α-arylation of carboxylic aids and secondary amides with aryl halides. Both of the presented coupling processes occur with a variety of carboxylic acids and amides and with a variety of aryl bromides containing a broad range of functional groups, including base-sensitive functionality like acyl, alkoxycarbonyl, nitro, cyano, and even hydroxyl groups. Five commercial drugs were prepared through this method in one step in 81-96% yield.

Exploring Vibration Transmission Rule of an Artificial Spider Web for Potential Application in Invulnerability of Wireless Sensor Network.

Significant similarities exist between a spider web and wireless sensor network in terms of topology. Combining the unique advantages of the spider web in nature, such as invulnerability and robustness, with communication technology of a wireless sensor network presents high research value and broad development prospects. In this paper, a sort of a spiral artificial spider web based on 3D printing and its associated vibration testing device is proposed, which is used to study the transmission rule of vibration information of the spider web under given excitation conditions.

Enantioselective α-functionalizations of ketones via allylic substitution of silyl enol ethers.

The enantioselective construction of carbon-heteroatom and carbon-carbon bonds that are alpha to ketones leads to the formation of substructures that are ubiquitous in natural products, pharmaceuticals and agrochemicals. Traditional methods to form such bonds have relied on combining ketone enolates with electrophiles. Reactions with heteroatom-based electrophiles require special reagents in which the heteroatom, which is typically nucleophilic, has been rendered electrophilic by changes to the oxidation state.

Trimethylphosphate as a Methylating Agent for Cross Coupling: A Slow-Release Mechanism for the Methylation of Arylboronic Esters.

A methyl group on an arene, despite its small size, can have a profound influence on biologically active molecules. Typical methods to form a methylarene involve strong nucleophiles or strong and often toxic electrophiles. We report a strategy for a new, highly efficient, copper and iodide co-catalyzed methylation of aryl- and heteroarylboronic esters with the mild, nontoxic reagent trimethylphosphate, which has not been used previously in coupling reactions.